Mobile machines, such as, for example, dozers, tractors, rippers, plows, and/or scrapers, often include one or more material engaging implements configured to manipulate material, e.g., transport, cultivate, dig, or otherwise disturb the ground and/or material piles. The material often includes soil, rocks, sand, and/or materials which affect the material's characteristics, e.g., hard, soft, rocky, homogeneous, or other properties known in the art. Machines, powered by an engine operatively connected to one or more traction devices, typically traverse a site that has changing terrain, such as, varying grades, e.g., inclines or declines, and the material associated with the site often has varying characteristics, e.g., soft soil changes to hard soil or a mixture of soil and relatively small rocks changes to a mixture of soil and relatively large rocks. The magnitude of resistance an implement applies to machine movement is influenced by the depth at which an implement engages the material and the characteristics of the material. That is, an implement that engages soft soil at a shallow depth applies relatively less resistance to machine movement than an implement that engages hard soil at a deep depth.
Too much or too little resistance may be undesirably cause machine vibration or poor engine operation, e.g., the loading on the engine is too large or small. Typically, manual control of a machine and associated implements with respect to changing terrain and changing material characteristics is complicated and requires a significant amount of skill. An operator typically adjusts the depth an implement engages the material or penetrates the surface thereof, e.g., a depth of cut, in response to changing material characteristics so as to operate the machine within a desirable set of conditions, e.g., below an engine torque limit.
U.S. Pat. No. 4,518,044 (“the '044 patent”) issued to Wiegardt et al. discloses a vehicle with a control system for raising and lowering an implement. The control system of the '044 patent senses parameters, including wheel slip, engine speed, and draft force. The control system of the '044 patent determines parameter error signals as a function of the sensed parameters and predetermined threshold values. The parameter error signals are combined into a composite error signal representing a vehicle load. The system of the '044 patent also determines a position error signal as a function of a desired operator position command and a sensed implement position. The system of the '044 patent compares the composite load error and the position error and operates to raise or lower the implement in response to the more positive error.
The reactionary control of the system of the '044 patent may inadequately respond to both steady state and transient load changes. Additionally, the composite error of the system of the '044 patent may be undesirably slow with respect to rapid changes in loads encountered by the implement. Furthermore, the system of the '044 patent may determine the composite error via a complex algorithm.
The present disclosure is directed to overcoming one or more of the shortcomings set forth above.